The present invention relates to a system for drilling and simultaneously installing a relatively large production casing along an invert underground arcuate path beneath an obstacle.
Various types of systems for drilling and installing production casings along an invert underground arcuate path beneath an obstacle have been developed by this inventor. Such systems are perhaps typified by U.S. Pat. No. 3,894,402, issued to this inventor. In such systems, a pilot hole is first drilled at least partially along the preferred path beneath the obstacle, as described in U.S. Pat. No. 3,878,903. A larger production casing is then installed along the path of the original pilot hole.
The systems described above have represented a substantial advance in the state of the art of drilling technology, as described in the above-referenced patents. However, it has been found that certain difficulties arise when relatively larger production casings, typically in excess of 16 inches in diameter, are to be installed along the length of the pilot hole. An initial problem is that certain of the techniques previously used by this inventor require that the production casing itself be rotated. However, the rotation of a large diameter production casing when it is installed along a curved path is often unfeasible because of the strain on the casing and such techniques can only be used with smaller casings. Even when techniques are employed in which the production casing itself is not rotated, the fact that the production casing is much larger than the drill string occupying the pilot hole makes it difficult to have the production casing flex so that it can follow the drill string. Production casings now known and used are linear, and must actually flex to follow the pilot string along the curved path, which is quite difficult and often impossible when the production casing is of relatively large diameter.